You have to take your time when you're baking, but not when making icing. In the time it takes to bake an item, you can prepare a from-scratch icing or frosting in the piping bag or warm and ready to drizzle. The only difference between buttercream -- best for pastry fillings and cake icings -- and a powdered-sugar icing, best for cupcake glazes and other small jobs, is butter, and you can have either set to decorate well before the oven cools.
Sift 1 cup of powdered sugar into a mixing bowl for every 1/2 cup of icing you want to make.
Drizzle milk into the sugar, 1 tablespoon at a time, while stirring. You need 2 tablespoons of milk for a stiff icing and about 3 to 4 tablespoons of milk for a pourable icing.
Stir a drop or two of extract per cup of frosting, if desired. Vanilla works with everything; use other flavors, such as orange, lemon and cinnamon, to match the baked good as needed.
Sift 4 parts powdered sugar into a bowl and set it aside. You need about 4 cups of sugar to make the icing for a 9-inch cake.
In a separate mixing bowl, beat 1 part room-temperature butter and 1 teaspoon of vanilla extract until creamy using a stand-mixer or hand-mixer.
Beat in the sugar, 1/2 cup at a time, with the mixer on low until it's incorporated and smooth. Scrape down the sides of the bowl every minute or so.
Beat in just enough milk to cream the icing; about 1 tablespoon per cup sugar should do it. Use the icing as is or store it up to 10 days in the refrigerator with a piece of plastic wrap covering the surface.